I got this idea from a friend, but basically what you do is post something that's associated with the post above, and give a brief explanation (in parentheses) of why they're associated. Here's an example below:

Start: Japan
Reply 1: Anime (A lot of anime are from Japan)
Reply 2: Art (Arts draw anime)
Reply 3: Statues (Statues are a type of art)
Reply 4: Roman Empire (There are a lot of famous statues in the Roman Empire)
Reply 5: History (The Roman Empire was rich in historical values)
Reply 6: Pearl Harbor (Pearl Harbor was an important historical event)
Reply 7: Hawaii (That's where Pearl Harbor is located)
Reply 8: Beaches (Hawaii is famous for its beaches)
....
etc.
And so on..........

Anyways I think everyone gets the idea now, and it'll be fun to see what people come up with. If someone posts but didn't follow the rules, such as Potatoes then Airplane, or at least didn't give a reasonable explanation, or simply is just spam, then post a reply to the one that previously made sense.